Modern telecommunication networks can provide a number of different types of services to users. For example, a user may, at any particular time, be communicating using a portable telephone, watching television using a set-top box, or interacting with a personal computer. Further, the user may be physically present in any number of different locations (i.e., the user may be at home, at work, or someplace else).
The on/off state of a user's communication devices, the physical location of the user, the user's presence and availability via various devices, and possibly other information relating to the user's state, such as user preferences, may be useful to other people or businesses with whom the user interacts.